The primary objective is the understanding of dynamic processes involving bile salts, in cholesterol gallstone formation and dissolution, and in digestion. Cholesterol solubilization studies will be undertaken in the low flow region, and solubilization experiments with intestinal lipids will be extended to liquid lipids. A survey of the effects of a variety of additives on cholesterol growth rates is planned. The effect of micelle size on cholesterol growth rate and induction time will be studied. Detergent aggregation as a function of molecular size of the detergent will be studied with specific ion electrodes. The bile salt-lecithin-cholesterol mixed micellar system will be studied in detail. Selective surfactant ion electrodes will be used in conjunction with a series of selective cation electrodes to determine competitive binding of various counterions, particularly calcium and heavy metal ions. An attempt will be made to develop a solid state electrode, and the use of microelectrodes will be explored.